20-minute delay prior to screen display

Since 2/18/14 my wife's Gateway Desktop running Vista Home Premium x64 SP2 with all updates suddenly developed a problem which has persisted thru today (3/3/14) in spite of running virus scans, chkdsk, memory and disk diags and a whole bunch of changes to power management changes. There were no programs installed on 2/17 or 2/18 but there may have been a windows update. Nothing out of the ordinary shows up in the event logs.

The system seems to run fine all day (most days) properly going into cpu and monitor sleep mode. It wakes quickly when the mouse is moved or a key is pressed. However at 6 or 7 am tapping on the space bar causes the screen to flash the current window and then go black. No amount of tapping keys wakes the monitor. (I did not try CAD to get to the task monitor). 20-30 minutes later the screen is back to sleep mode (display light is blinking) and pressing the keyboard or moving the mouse wakes the dispay and all is well for the rest of the day (most days).

So, most of the time, this appears to be a night time problem. In addition to several system tasks I wake the computer at 3:50am every morning to run an image backup which completes properly. Every couple of days the problem also occurs durring the day.

I have read most of the threads on this forum related to sleep/wake/death screen issuse but do not see anything identiacal to this issue.

I would make sure that my power settings were set to ALWAYS ON for everything -- the computer would not ever go into hybernate or sleep mode unless I told it to; the monitor would never go dark unless I manually turned it off; and the screen saver wouldn't darken the monitor. If this fixes the problem, then I would say you have a monitor which is going bad.

You may be right about a Windows update. You can uninstall whatever updates were installed immediately prior to when the problem started.

But to me, the most likely cause is a defective video card or monitor. If you have a spare video card, you could install it and use it rather than the one you are currently using, to see if the problem goes away.

Also, if you have a spare monitor, you could use it rather than the one you are currently using.

Doing one of these things at a time will hopefully let you know what is the source of the problem.

Thanks for the support.
I have already done what mrjimphelps suggested; basically turned off cpu and monttor sleep leaving only disk sleep.
I am convinced that the problem is very old 24" LCD monitor; the graphics card is 8 months old.
I plan to swap monitors to see what happens.

I had a similar problem last autumn, except it occurred when switching on the PC in the morning, or after a reboot during the day. The delay of 2-3 minutes extended to about 15 minutes over a few weeks.

It was suggested I should try another monitor, and sure enough, when it was connected to the wife’s PC it took just as long to start, whereas her monitor was trouble free on mine. So, my ageing XP was replaced last year, instead of early this year as planned.

It appears that you are saying that when you swapped monitors, you found that the monitor was bad (the problem followed the monitor; it didn't stay with the PC), and as a result, you replaced the computer?

If the problem happened on your wife's PC while your monitor was connected to it, and it no longer occurred on your PC when your wife's monitor was connected to it, then there was no reason to replace the computer; the monitor was what had the problem.

Thanks to all of you who offered sugestions for my queston about 20 minute delay on waking up from sleep which I posted 3/3/14.
The problem turned out to be a display monitor with was failing. Replacing it resolved all of the problems.